Search

Designing solid-state electrolytes for proton batteries at moderate temperatures is challenging as most solid-state proton conductors suffer from poor moldability and thermal stability. Crystal–glass transformation of coordination polymers (CPs) and metal–organic frameworks (MOFs) via melt-quenching offers diverse accessibility to unique properties as well as processing abilities. Here, we synthesized a glassy-state CP, [Zn3(H2PO4)6(H2O)3](1,2,3-benzotriazole), that exhibited a low melting temperature (114 °C) and a high anhydrous single-ion proton conductivity (8.0 × 10−3 S cm−1 at 120 °C). Converting crystalline CPs to their glassy-state counterparts via melt-quenching not only initiated an isotropic disordered domain that enhanced H+ dynamics, but also generated an immersive interface that was beneficial for solid electrolyte applications. Finally, we demonstrated the first example of a rechargeable all-solid-state H+ battery utilizing the new glassy-state CP, which exhibited a wide operating-temperature range of 25 to 110 °C., Melt-quenched coordination polymer glass shows exclusive H+ conductivity (8.0 × 10−3 S cm−1 at 120 °C, anhydrous) and optimal mechanical properties (42.8 Pa s at 120 °C), enables the operation of an all-solid-state proton battery from RT to 110 °C.

The crystal–liquid–glass phase transition of coordination polymers (CPs) and metal–organic frameworks (MOFs) offers attractive opportunities as a new class of amorphous materials. Unlike conventional glasses, coordination chemistry allows the utilization of rational design concepts to fine-tune the desired properties. Although the glassy state has been rare in CPs/MOFs, it exhibits diverse advantages complementary to their crystalline counterparts, including improved mass transport, optical properties, mechanical properties, and the ability to form grain-boundary-free monoliths. This Review discusses the current achievements in improving the understanding of anomalous phase transitions in CPs/MOFs. We elaborate on the criteria for classifying CP/MOF glasses and comprehensively discuss the three common strategies employed to obtain a glassy state. We include all CP/MOF glass research progress since its inception, discuss the current challenges, and express our perspective on future research directions.

Prussian blue analogues (PBAs), a class of microporous crystalline coordination frameworks, are long known for their diverse properties in porosity, magnetic, charge transport, catalysis, optics, and more. Versatile structural composition and the ability to control defect ordering through synthetic conditions offer opportunities to manipulate the functionality in the crystalline state. However, developments in Prussian blue analogues (PBAs) have primarily revolved around the ordered crystalline state, and the glassy state of PBAs has not yet been explored. Here we report the discovery of a disordered glassy state of the PBA via mechanically induced crystal–glass transformation. We found the preservation of metal–ligand–metal connectivity, confirming the short-range order and semiconductor behaviour, exhibiting an electronic conductivity value of 0.31 mS cm−1 at 50 ˚C. Mechanical-induced glass transformation also triggers changes in electronic states, where electroneutrality is compensated by introducing unconventional CN− vacancies. Partial disorders and ligand vacancies in recrystallized PBA give rise to an enhanced porosity, inaccessible in the crystalline parent. The present work also established a correlation between the mechanical stress required to initiate crystal–glass transformation and intrinsic mechanical properties, which are controlled by the vacancy/defect content, the presence of interstitial water, and the overall composition of PBAs.

The unusual intercalation phenomena of alkali cations (Li+, Na+, K+, Rb+, and Cs+) in the sulfate-based electrolyte on the electrochemical behavior of birnessite-type layered-manganese oxide nanosheets with Li-intercalated cation (Li-MnO2) were studied by in situ electrochemical synchrotron X-ray Absorption spectroscopy. Li-MnO2 exhibits the highest charge storage capacity in Na2SO4(aq), followed by Li2SO4, K2SO4, and Cs2SO4, respectively. Whilst, it does not exhibit the charge-storage characteristics in Rb2SO4 as the solvated Rb+ could not intercalate into the lamellar structure of birnessite. Understanding unusual intercalation phenomena can be useful for further development of the electrochemical capacitors.

The sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is a crucial issue that limits a practical utilization of metal-air batteries. Manganese oxides with various structures, δ-, β-, α-, or γ-MnO2, have been studied and reported as electrocatalysts for the ORR and/or OER. Here, we have suggested birnessite-typed layered manganese oxides (δ-MnO2) with their sheet-like structure and interlayer spacing of ca. 7 Å containing different alkaline intercalated cations within the layers as bifunctional electrocatalysts. Surprisingly, the experimental results together with a fundamental explanation by density functional theory (DFT) calculations show that the intercalated cations between layers of the birnessite (Bir) play an important role on the ORR and OER catalytic activities which have the activity trend as follow: Li-Bir > Na-Bir > K-Bir > Rb-Bir > Cs-Bir.[1] Apart from the fundamental study, primary Zn-air batteries with these materials are also demonstrated. Zn-air battery with the Li-Bir catalyst shows the highest performance among these catalysts. Moreover, we also integrated the Li-Bir with reduced graphene oxide (rGO) as a composite to improve the electronic conductivity of the MnO2. The mechanical rechargeable Zn-air battery with Li-Bir/rGO composite as an air electrode demonstrates better performances than the Zn-air battery with a pristine Li-Bir catalyst. Interestingly, even the Zn-air battery with the Li-Bir/rGO composite (0.687 V) shows higher potential gap between discharge and charge potentials than state-of-art Pt/C+RuO2 (0.667 V) in the first cycle (2 hours per cycle), however, the Zn-air with our composite catalyst exhibits smaller potential gaps of 0.697 V and 0.719 V (0.720 and 0.761 V for Pt/C+RuO2) at the second and third cycles, respectively. In addition, our mechanical rechargeable Zn-air battery displays an impressive cyclability of discharge-charge processes (10 minutes per cycle) of 500 cycles or over 83 hours at a current density of 2 mA cm-2. Therefore, the Li-bir/rGO composite could be used as a bifunctional electrocatalyst in a practical application for Zn-air batteries. Reference [1] S. Kosasang, N. Ma, P. Wuamprakhon, N. Phattharasupakun, T. Maihom, J. Limtrakul, M. Sawangphruk, Chem. Commun. 2018, 54, 8575.

Lithium-sulfur battery (LSB) is a promising candidate as a conventional lithium-ion battery replacement due to its high theoretical specific capacity and high energy density together with additional advantages of low cost, abundance, and environment friendliness. However, LSB still suffers from many issues including natural insulator of active sulfur and final product of Li2S, polysulfide shuttle effect, and 80% volume expansion during cycling which are causes of capacity fading in the LSB. To fix the mentioned issues as well as improve performances of LSB, carbon interlayer has introduced between a sulfur cathode and separator to suppress lithium polysulfide diffusion and act as an upper current collector. Here, we prepare surface modified carbon fiber paper (CFP) via a simple amide coupling reaction with various amine reactants to study the effect of functional groups on the surface of the CFP on LSB performances. LSB with modified CFPs as interlayers show significant higher specific capacity than LSB without interlayer due to the chemisorption ability between functional groups on the CFP surfaces and lithium polysulfide intermediates. The LSB with modified CFP by 4-aminobenzoic acid interlayer exhibits the highest specific capacity along with long cyclability observed from high capacity retention of 88.5% and Coulombic efficiency above 98% after 200 cycles. Furthermore, the lithium polysulfide chemisorption capabilities of each functional group are fundamentally explained via density functional theory (DFT) calculations through the binding energy between functional groups and polysulfide intermediates. More interestingly, we also prove that the excellent performance of the LSB with 4-aminobenzoic acid interlayer is due to the strong lithium bond of S-L…O coupled with hydrogen bond of S…H-O.

The sluggish kinetics of oxygen reduction reaction (ORR) is a critical challenge for metal-air batteries and fuel cells. To increase the reaction rate, the high-efficient electrocatalysts are needed. Among various catalysts, platinum and its alloys are investigated as the best catalyst for the ORR. However, the Pt-based catalysts suffer from many disadvantages, including excessive cost, scarcity, and poor stability. In this work, layered manganese oxides, Li-birnessite, Na-birnessite, K-birnessite and their composites with graphene aerogel were used as the ORR catalysts. The ORR catalytic activity of these materials has been studied using rotating disk electrode (RDE) in O2-saturated and Ar-saturated KOH solution. The linear sweep voltammogram (LSV) curves at scan rate of 10 mVs- 1 show that the Li-birnessite/graphene aerogel provided the best catalytic performance with an onset potential of 0.99 V (V vs. RHE), half wave potential of 0.66 V (V vs. RHE), limiting current density of 5.60 mA cm- 1 (at a rotation rate of 1600 rpm), and Tafel slope of 104.3 mV dec- 1, which is comparable to the Pt catalyst. Moreover, the electron transfer number per oxygen molecule (n) calculated by Koutechy–Levich (K–L) equation is ~ 4, indicating a 4-electron pathway for ORR and suggesting the Li-birnessite manganese oxide coated on graphene aerogel as a high-efficient ORR catalyst.

We propose a new concept of using a redox additive potassium ferrocyanide in 1-butyl-1-methylpyrrolidinium dicyanamide ionic liquid electrolyte for high-performance supercapacitors. Coupling with a unique nanostructure of N-doped reduced graphene oxide, the supercapacitor using this new hybrid electrolyte exhibits the excellent specific energy and power of 89 Wh kg-1 and 3677 W kg-1, respectively. An excellent long-term stability is demonstrated up to 10000 cycles of charge-discharge with 87% capacitance retention.